Patent GB-760526-A (GB)
Title: Methods of and apparatus for making abrasive tools
IPC: B24D3/08
Filed: 1954-06-11
Abstract: 760,526. Abrasive tools. BOART PRODUCTS, SOUTH AFRICA, Ltd. June 11, 1954 [Nov. 25, 1953], No. 17238/54. Class 60 A patterned abrasive tool is made by covering a backing surface with a thin layer of adhesive and causing abrasive particles to pass through a patterned screen held in close proximity to the backing surface. A blank 3 in the form of a ring is coated, over the entire working surface, with a very thin layer of adhesive 8. The blank 3 is then placed in a ring 41 of insulating material and clamped therein by thumb screw 43. The ring 41 carrying the blank 3 is then mounted in apparatus comprising an annular base member 47 of insulating material recessed to receive an annular metal tray 49 containing abrasive particles 10, e.g. diamond powder 200-400 mesh or up to 80-mesh. The abrasive particles may be mixed with another powder of water soluble material, e.g. sodium sulphate, which at a later stage in the process is dissolved as described in Specification 720,844. Electrical contact with the tray 49 is made by a connector screw 57 threaded through base member 47 and connected to a high voltage lead 63. A fixed centre plug 53 of insulating material fits within base member 47. Screens 45, 46 with a pattern of slots are laid across the upper surfaces of base member 47 and centre plug 53; the screen 45 is of brass 0.25 mm. thick, while screen 46 is much thinner, e.g. 0.075 m.m. The slots in the lower screen 45 are narrower than those in the upper screen 46; the screens may be permanently fastened together, e.g. by soldering. Alternatively a single screen may be used. Spacing shims 65 of paper or metal are placed between the upper surface of screen 46 and the lower surface of ring 41 carrying the blank 3. A removable centering plug 67 of insulating material has a metal handle 69 the lower end of which passes through center holes of screens 45, 46 and into bore 55 of centre plug 53. The thumb screw 43 is connected by a clip 71 to a high voltage lead 64. The high voltage source is then switched on, causing the particles to jump upwardly, some passing through the screens 45, 46 to be held by the adhesive on the blank 3; the electrostatic depositionorients the particles. Where orientation is not important, the blank may be positioned with its working face upwards, the screens placed over the blank, and abrasive powder sifted on to the blank through the screens. The blank and ring 41 are removed from the apparatus, and the blank 3 is then taken from the ring 41. After the adhesive has set the blank is immersed in water to dissolve the soluble particles. The non-working surfaces of the blank are then covered with insulating plastic material, e.g. by immersion; metal 13, e.g. copper, is electrolytically deposited on the blank 3 to a, thickness equal to the desired protrusion of the particles, and a thicker layer 14, e.g. of nickel or iron, is then deposited to completely cover the particles 10. The electrodeposited metal is then all removed from the blank and soldered or otherwise permanently fastened to a backing plate 2, and the layer 13 of copper etched away so that the abrasive particles 10 protrude from the metal bond. The backing plate 2 may be secured to the metal 14 prior to removing the electrodeposited material from the blank 3. For forming a pattern of abrasive particles directly on to the backing plate of a tool, the first layer 13 is omitted, the layer 14 being deposited directly on to adhesive layer 8. The assembly is then heated to set and cure the adhesive which is preferably plastic; the layer 14 is of such depth that the particles 10 project therefrom; alternatively part of the layer 14 may be etched away partially to expose the particles.